1. Field
Example embodiments relate to methods of driving an active display device, which may have improved electric reliability.
2. Description of the Related Art
An active display device includes a switching transistor for controlling operations on each pixel. A thin film transistor (TFT) is generally and widely used as a switching transistor for the active display device. For example, at least one TFT is included in one pixel, and such a TFT may be classified into a silicon-TFT, an oxide TFT, an organic TFT, or the like, based on the type of semiconductor material used as a channel material. Recently, the oxide TFT, having a quicker switching speed, is generally used as the switching transistor.
A desired voltage is charged in a pixel unit for a predetermined period of time by a current flowing through a channel of the TFT (switching transistor) connected to each pixel. The charged voltage is maintained by turning off the channel after the predetermined period of time. In the case of an active matrix organic light-emitting display (AMOLED), a duration of turning on the TFT is determined by a driving frequency and resolution. If the driving frequency is 120 Hz and the resolution is a full high definition (HD) level, one TFT is turned on for 1/120/1080=7.7 μs. Also, the TFT is turned off for the remaining time of one cycle (1/120=8.3 ms). Accordingly, the TFT is turned off for the majority of time in the active display device.
Since an amorphous silicon TFT or an oxide semiconductor TFT mostly has an n-type semiconductor characteristic, a negative gate voltage is applied to turn off the TFT. Accordingly, the negative gate voltage is continuously applied to the turned off TFT in the active display device. However, if the negative gate voltage is continuously applied to the TFT for a certain period of time, a threshold voltage of the TFT may move in a negative direction. As a result, a leakage current may increase while the negative gate voltage is being applied. Such movement of the threshold voltage may be intensified if light is incident on the switching transistor. If the leakage current increases, the resolution of the active display device may deteriorate.